The invention is directed to equipment for use in racket sports, in particular a tennis-racket, comprising a racket frame tentered with tensioned strings, a handle portion, and an outer shell made of synthetic plastic materials at least partially embracing the racket frame.
There are several known processes for producing racket frames. It is known from DE-OS No. 33 43 889 to assemble such a racket frame of hollow profile by subdividing the plane of the tensioned strings. For the purpose of reliably providing the required strength of such hollow profiles, there can either be used a metallic material or a correspondingly highly reinforced synthetic plastic material. In both cases, the outer surface of the racket requires extensive machining to obtain a smooth surface. Several grinding and varnishing steps are required to be subsequently applied to the frame decorations or printings, which result in a relatively expensive finishing operation. Furthermore, there are environmental effects because of the solvent vapors from varnishes, which are usually applied by spraying. The varnish layers applied onto the outer surface of such rackets are relatively thin and withstand mechanical stress for only a limited time interval.
Frames of tennis rackets are subject to several kinds of mechanical stress. Any exerted bending stress or torsion stress may result in fracture when fiber-reinforced synthetic plastic materials are used. Varnish layers applied to the outer surface of such frames contribute nothing to stabilizing the frame, and if the frame fractures, there exists a substantial risk of injury from protruding frame parts or parts of reinforcing inserts.
FR-A No. 2 326 211 discloses a component part consisting of synthetic plastic material, which is pressed onto the racket frame in a form-locking manner. This component part represents a protective strip which is made in one piece and has its free ends separated from one another
DE-AS No. 2 328 371 discloses a racket composed of metal and synthetic plastic material and having an inner flange and outer flange of the racket frame coated with protective layers of synthetic plastic material. These protective layers of synthetic plastic material cover the surfaces of both flanges and have a definite modulus of elasticity.
U.S. Pat. No. 4,042,238 discloses a sheathing for a racket consisting of synthetic plastic material, i.e. ABS (acrylonitrile butadiene styrene) copolymer.
Frame construction using shell portions must correspondingly be reinforced in the shell portions representing load-carrying constructional elements of the frame. Thus, these portions cannot have a smooth outer surface suitable for screen printing or lettering. All such frame constructions require extensive finishing operations. From AT-PS No. 362 269, it is known to assemble a frame from a plurality of wall members, wherein tongue-in-groove joints are used for the front walls and side walls for the purpose of improving stability. Also in such frame constructions, which require extensive assembling operations, the box-frame construction of the frame must fulfill a load-carrying function requiring the designing of synthetic plastic materials for the load-carrying function. The synthetic plastic materials must be of relatively high hardness, and thus there is an increased danger of fracturing. Correspondingly reinforced synthetic plastic materials do not have a smooth outer skin. Therefore, in addition to complicating the assembly of such rackets, expensive finishing operations are needed for producing a smooth outer surface.